Color projection transparencies

ABSTRACT

Sheet material, which forms a color projection transparency when imaged with salicylic acid vapor, achieves improved color intensity and fade-resistance from a combination of protonatable color progenitor and oxidizable leuco cyanine or styryl dye precursor.

United States Patent [191 Deyak Dec. 24, 1974 COLOR PROJECTION TRANSPARENCIES [75] Inventor: Frank L. Deyak, Stillwater, Minn.

[ 73] Assignee: Minnesota Mining & Manufacturing Company, St. Paul, Minn.

[58] Field of Search 117/362, 36.8; 106/288 B [56] References Cited UNITED STATES PATENTS 12/1969 Berg et al. 117/362 Sugahara et al 106/288 B Huffman 117/368 Primary Examiner-Thomas J. Herbert, Jr. Attorney, Agent, or Firm-Alexander, Sell, Steldt & DeLaHunt [5 7] ABSTRACT Sheet material, which forms a color projection transparency when imaged with salicylic acid vapor, achieves improved color intensity and fade-resistance from a combination of protonatable color progenitor and oxidizable leuco cyanine or styryl dye precursor.

5 Claims, N0 Drawings COLOR PROJECTION TRANSPARENCIES This invention relates to the formation of colored images and in one major aspect to the projection of lightimages in color and to materials for use therein.

The preparation of color projection transparencies, by a process involving the acidification of transparent films containing protonatable color precursors by application of acid vapors at areas defined by imaged original, has been described. For example, in Berg et al, U.S. Pat. No. 3,483,013 the transparent film may consist of a protonatable chromogenous dye-forming color progenitor in a vinyl halide resin binder coated on a thin transparent supporting film. An acid source sheet, for example, containing salicyclic acid is placed against the coating and is heated thermographically at image areas. The acid is volatilized and reacts with the color progenitor to form a colored image. Upon removal of the acid source sheet there remains a color projection transparency which retains its color for as much as 2 to 4 hours on the overhead projector, but thereafter slowly fades until the visibility of the projected image is eventually lost.

The present invention likewise makes use of an acid source sheet such as that described in Berg et al., to-

gether with a transparent film containing color-forming bodies, the two sheets being preferably pre-assembled together with a removable intermediate separator sheet in an integrated structure for convenience in packing and using. The films of the present invention produce images which are initially strongly colored and-which remain strongly colored under longcontinued exposure.

The invention makes use of a novel combination of color-formers. One of them represents a known -trimethyl-class, herein referred to also as Class A, of protonatable color. progenitors which on reactive contact with a weak acid are promptly converted onehalf color-bodies. The other represents a second class (Class B) of oxidizable amine color-forming compounds which only gradually develop a moderately strong color when first acidified with an acid such as salicylic acid. Surprisingly, it has now been found that the presence of the protonatable color progenitor of the first class in association with a compound of the second class results in the formation of a much stronger color than would be expected from a simple additive effect. Additionally, it is discovered in many instances that exposure to illumination either during or subsequent to acidification, e.g., in the thermographic copying process or on an overhead projector, still further increases thecolor strength or density and at the same time confers improved resistance to fading under tropic room accelerated aging test conditions as well as under normal aging.

The two color-forming components are themselves Substantially colorless. They are conveniently applied to a suitablesubstrate from solution in a volatile liquid vehicle containing a film-forming binder. A transparent thin film, e.g., polyethylene gycol terephthalate polyester, serves as a preferred form of permanent substrate where the product is to be used as a projection transparency, but paper or other non-transparent substrates or carriers may be used where transparency is not a requirement. The binder may itself serve as a carrier where exceptionally thin sheet structures are desired.

The liquid mixture is spread uniformly over the permanent or temporary substrate surface and the volatile vehicle removed by evaporation.

In a preferred structure an acid source sheet and a color-forming film in face-to-face relationship are ad'- herently tabbed or fastened together along one margin and with a thin acid-impervious separator sheet or film loosely laid between. Glassine or non-porous paper, preferably coated with a thin layer of vinyl chloride polymer or the like, makes an effective separator, To make a transparency, the separator film is. first withdrawn, leaving the coated surfaces in contact. A graphic original is placed against the couplet and is briefly subjected to intense radiation in a thermographic copying machine. A colored image of the original is produced on the color-forming sheet, which is then removed from the acid source sheet, being provided with a row of perforations adjacent the margin for that purpose. The imaged sheet serves as a color projection transparency. The color density of the image is initially high and is maintained at a high level both during prolonged projection and under prolonged exposure to heat and humidity in accelerated aging tests.

Protonatable chromogenous dye-forming color progenitors useful in the sheet materials of the present invention are represented by compounds such as the following:

N-bis-(p-dimethylaminophenyl)-methyl morpholine N-(n-bis-(p-dimethylaminophenyl)-methyl) benzenesulfonamide N-(n-butyl-) N-(bis (4-dimethylaminophenyl) methyleneurea 2-(p-hydroxystyryl)-3,3-dimethylindolenine bis-(p-diethylamino) triphenyl hydroxymethane p-(N-methyl-N-cyanoethyl) styryl-3,3-

dimethylindolenine as described by Berg et al. They convert to a colored modification promptly upon treatment with salicylic acid vapor.

, The second class of color-forming materials employed in the practice of the invention is described in application Ser. No; 347,193 of George Van Dyke Tiers and Joseph A. Wiese, Jr. filed on Apr. 2, i973, and entitled: Reduced Styryl-Cyanine Dye. These materials have been defined as N-hydrocarbylsubstituted dihydroheterocyclic tertiaryamines having a 2-(or'4-)(omega(nuclearly substituted cyclic)) -vinylenyl substituent, or simply as N-hydrocarbylsubstituted dihydroheterocyclic amines. They are capable of being oxidized in an anionogenic environment to yield colored products which are styryl or cyanine dyes. Conveniently prepared by chemical reduction of such dyes, e.g., with sodium borohydride, these Class B compounds have as their basic structure the linkage wherein R is lower alkyl and R R, and R either separately or in combination represent skeletal structures including a total of at least about six carbon-to-carbon double bonds in conjugate arrangement with the N-C bond. Typical and preferred examples of these Class B compounds include the following:

2-('4-dimethylaminostyryl)-1,3,3-trimethylindolene 2-(2-pyrrole styryl)-1,3,3-trimethylindolene 2-(3-indolenostyryl)-1,3,3-trimethylindolene 2-(4,4-bis-(4-dimethylaminophenyl))-butadienyl- 1,3,3-trimethylindolene 2-(p-di-B-chloroethylaminostyryl)-l ,3,3-

trimethylindolene 2-(2-( l-benzyl-3-indolyl)-vinylenyl)-1,3,3-

trimethylindolene Z-(p-dipenylaminostyryl)-1,3,3-trimethylindolene and others are listed in the above-indentified application Ser. No. 347,193.

Compounds of each of the above-defined classes, when separately applied with a binder as a thin coating on a carrier film and imaged by treatment with salicylic acid vapor, are found to produce colored images. Those of Class A develop the color immediately upon treatment with the acid; with compounds of Class B, the color develops slowly over a period of several hours or days. With either class, color images of useful optical density may be attained. Surprisingly, the combination of compounds from the two classes yields a sheet material which not only produces'a strong color immediately upon treatment and remains strongly colored upon prolonged aging, but additionally shows an increase in color density over the anticipated sum of the color densities attributable to the two components considered separately. Furthermore the combination of these two materials, neither of which separately is appreciably sensitive to light, in many cases makes available a still further increase in color density when the sheet is strongly illuminated during or after imaging, as for example by image projection on an overhead projector immediately after image formation.

For most purposes it will be apparent that compounds of the first and second classes should be selected which produce color bodies having the same, or very nearly the same, color. in some instances it may be found necessary to employ mixtures of Class A or Class B dyes, or both, in order to obtain a desired continuity of color. Conversely, the selection is contemplated of materials which produce dissimilar colors, so that the original image color may change to a different color during continued image projection or upon aging.

Again, in most instances the amounts of colorforming materials will be proportioned to provide and maintain a substantially constant image density sufficient to project a colorful and easily visible image; but disproportionation of materials, to provide either increase or decrease in image density during continued projection or upon aging, is likewise contemplated.

Polyester films as above described are heat-resistant, dimensionally stable, and transparent, and are preferred; but films of cellulose or derivatives, vinyl polymers, and other film-forming materials are also useful. Likewise the film-forming binders may be selected from a wide variety of wellknown materials used for such purposes, including ethyl cellulose, vinylchloridevinyl acetate copolymers, cellulose acetate butyrate, polyvinylacetate, polymethylmethacrylate, polyvinylbutyral, styrene-acrylonitrile copolymer.

The following Examples, in which all proportions are given in parts by weight unless otherwise noted, will serve further to illustrate but not to limit the practice of the invention.

EXAMPLE 1 Color projection transparency films are prepared by coating transparent polyester film with solutions in acetone of styrene-acrylonitrile resin (Tyril 880 binder and colorforming materials. The coatings are applied at a thickness of two mils (0.05 mm.) and dried in a forced air oven maintained at 180 F. Segments of the films are placed against an acid source sheet as previously described and the composites are locally heated by thermographic copying procedures. A portion of each segment is placed on an overhead projector and illuminated for fifteen minutes. The optical density of the image is measured for both segments, and is reported after correction for background density which is usually on the order of 0.01-0.15. The segments are then placed in an accelerated aging chamber and held for several days, i.e., until each reaches substantially constant color value, under conditions of 105 F. and relative humidity, whereupon the image density is again determined and recorded.

Compound A is N-(n-butyl)-N-(bis- (dimethylaminophenyl) methylene urea), a protonatable color progenitor which on protonation produces a magenta color.

Compound B is 2-(4-dimethylaminostyryl)-l,3,3- trimethylindolene, an oxid'izable N-hydrocarbyl monosubstituted dihydroheterocyclic tertiary amine color precursor. Oxidation of this compound in an acidic medium likewise produces a magenta color.

The formulations and results are as follows:

The formulations and results are as follows:

It will be seen that exposure to light on the overhead projector has in some manner resulted in an increase in image density in sample No. 2. Furthermore the results show that the image density in sample No. 2 is greater than the sum of the densities in samples 1 and 3.

EXAMPLE 2 Transparencies are prepared and tested as in Example 1 except for substitution of compounds. Compound A is 2-(p-hydroxystyryl)-3,3-dimethylindolenine. Compound B is 2-( 2-pyrrole styryl)-1,3,3- trimethylindolene. The sheet produces a yellow image. The optical densities are as tabulated:

after 3 days before aging accel. aging normal pre-ill'd normal pre-illd l .65 .66 .48 .45 2 .71 .75 .55 .62 3 0 .06 .Ol .08

EXAMPLE 3 Same as Example 1 but wherein Compound A is N- bis-(p-dimethylaminophenyl)-methyl morpholine, and Compound B is 2(4,4-bis(4-dimethylaminophenyl))- butadienyl-l ,3,3-trimethylindolene. The image color is cyan. Optical densities are as tabulated:

dimethylaminophenyl)) butadienyl-l,3,3-triemthyl-5- chloroindolene. Formulations Nos. 1 and 3 are as in previous examples, but formulation 2 employs only onelhalf the previous amounts of compounds A and B. Densities are tabulated below:

after 4 days before aging accel. aging normal pre-illd normal pre-illd The mixture of dyes is shown to be more effective than the same total amount of either dye separately.

EXAMPLE 5 The relative amounts of N-bis(p-dimethylaminophenyl)-methyl) morpholine as Compound A and of 2-(4,4-bis) -4-dimethylaminophenyl))-butadienyl- 1,3,3-trimethylindoline as Compound B are varied in a series of coatings prepared and tested otherwise as in the preceding normal" examples and at daily intervals cient density or have deteriorated to below the desirable level. Similar trends may be determined for combinations of other specific compounds in similar manner. Images with density values of as little as 0.2 to 0.3 above background produce a visible image on the projection screen; but initial densities of at least about 0.80 are desirable for most purposes. Background densities are ordinarily not greater than about 0.04-0.05 and should in no case exceed about 0.20 for commercial acceptance. While the ratios of specific components're quired to provide these image density ranges may vary with the particular components. in general it is found desirable to employ the A and components in ratios of from about 2:1 to about 1:2 and in concentrations suchthat each in the absence of the other would be adequate to provide a readily visible image.

In the foregoing description the salicylic or equivalent acid is transferred to the color forming sheet from a separate removable acid source sheet. Integral sheets wherein the volatilizable acid is contained in a separate coating, preferably with an intermediate temporary barrier layer, are also useful particularly where projection transparency is not required.

What is claimed is-as follows:

1. Sheet material, which rapidly develops a longlasting color when first briefly subjected to vapors of salicylic acid, having an active color-forming stratum comprising a mixture of (A) a protonatable chromogenous dye-forming color progenitor and (B) a substantially colorless oxidizable Nhydrocarbyl-substituted dihydroheterocyclic amine precursor of a styryl or cyanine dye.

2. Sheet material of claim 1 wherein the 8" component is a 1,3,3-trimethyl indolene.

3. Sheet material of claim 1 including a transparent carrier film and wherein said stratum includes a polymeric film-forming binder.

as i di d, 40 4. Sheet material of claim 3 wherein said mixture Proportions of compounds Sample No. Compound A Compound B l .135 .100 2 .100 .100 3 .075 .100 4 .050 .100 5 .025 .100 6 .135 .200 7 .135 .075 8 .135 .050 9 .135 .025 (Ex.3) (.150) (.150) Image optical density after aging for, clays, Sample No. 0 1 2' 3 4 5 6 8 l .90 .86 .84 .82 .79 .77 .76 2 .86 .84 .81 .78 .75 .74 .73 3 .74 .72 .71 .69 .70 .69 .70 4 .65 .61 .55 I .54 .56 .57 .58 5 .44 .36 .35 .35 .36 .38 .39 6 .91 .86 .83 .80 .82 .81 .84 7 .92 .85 .82 .79 .77 .74 .69 8 .89 .81 .72 .63 .52 .47 .41 9 .90 .78 .67 .57 .44 .32 .28 (Ex.3) (.90) (.75)

Image densities of at least about 0.65-0.70 are desired for fully commercially acceptable images on color projection transparencies. It will be seen that after prolonged aging, samples 1-3, 6 and 7, as well as that of Example 3, meet this requirement, whereas the remaining samples have either failed initially to provide sufficontains thefA and B components in a ratio of from about 2:1 to about 1:2.

5. A copy-sheet assembly useful in making a color projection transparency copy of a graphic original by the thermographic copying process and consisting of a color-forming film member and an acid source sheet binder of a protonatable chromogenous dye-forming color progenitor and an oxidizable N-hydrocarbyb substituted dihydroheterocyclic amine precursor of a styryl or cyanine dye.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION PATENT NO. 3,856,552 DATED December 2, 197 4 INVENTOR(S) I FRANK L. DEYAK It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Col. 1, line 35, "tri-methylclass" should read first class Col. 1, line 38, "one-half" should read to Col. 1, line 60, after e.g. insert of Col. 4, line 6, "colorforming" should read color-forming Col. t, line 35, "The formulations and results are as follows: second occurrence should be omitted.

Col. 5, line 21, "onelhalf" should read one-half Col 6, line 26, "longlasting" should read long-lasting Col. 6, line 31, "Nhydrocarbyl-substituted" should read N-hydrocarbyl-substituted Signed and Scaled this ninth Day of December 1975 "[SEAL] Attest:

RUTH C. MASON C. MARSHALL DANN Arresting ff Commissioner oj'Parents and Trademarks 

1. SHEET MATERIAL, WHICH RAPIDLY DEVELOPS A LONGLASTING COLOR WHEN FIRST BRIEFLY SUBJECTED TO VAPORS OF SALICYCLIC ACID, HAVING AN ACTIVE COLOR-FORMING STRATUM COMPRISING A MIXTURE OF (A) A PROTONATABLE CHROMOGENOUS DYE-FORMING COLOR PROGENITOR AND (B) A SUBSTANTIALLY COLORLESS OXIDAZABLE N-HYDROCARBYLSUBSTITUTED DIHYDROHETEROCYCLIC AMINE PRECURSOR OF A STYRYL OR CYANINE DYE.
 2. Sheet material of claim 1 wherein the ''''B'''' component is a 1, 3,3-trimethyl indolene.
 3. Sheet material of claim 1 including a transparent carrier film and wherein said stratum includes a polymeric film-forming binder.
 4. Sheet material of claim 3 wherein said mixture contains the ''''A'''' and ''''B'''' components in a ratio of from about 2:1 to about 1:2.
 5. A COPY-SHEET ASSEMBLY USEFUL IN MAKING A COLOR PROJECTION TRANSPARENCY COPY OF A GRAPHIC ORGINICAL BY THE THERMOGRAPHIC COPYING PROCESS AND CONSISTING OF A COLOR-F0RMING FILM MEMBER AND AN ACID SOURCE SHEET RELEASABLY TABBED TOGETHER ALONG ONE COMMON MARGIN IN FACE-T0-FACE RELATIONSHIP AND AN ACID-IMPERVIOUS SEPARATOR SHEET REMOVABLY POSITIONED THEREBETWEEN, AND WHEREIN SAID COLOR-FORMING MEMBER INCLUDES A TRANSPARENT CARRIER FILM COATED WITH A MIXTURE IN A POLYMERIC BINDER OF A PROTONATABLE CHROMOGENOUS DYE-FORMING COLOR PROGENITOR AND AN OXIDAZABLE B-HYDROCARBYL-SUBSTITUTED DIHYDROHETEROCYCLIC AMINE PRECURSOR OF A STYRYL OR CYANINE DYE. 